Deck Material Calculator
To estimate deck materials, divide the deck width by one board width plus one gap and round up to get the rows of boards, multiply the rows by the deck length to get linear feet, add waste, and divide by the length of board you will buy. A 16 × 12 ft deck with 5.5-inch boards and a 0.25-inch gap needs 29 boards 16 ft long, 13 joists at 16 inches and 676 screws.
Your materials
Results update as you type.
- Boards to buy
- 29 boards
- 16 ft long
- Joists
- 13 joists
- 12 ft long
- Deck screws
- 676 screws
- Board cost
- —
- Add a price per board to see the cost.
How it adds up
-
Deck area 192 sq ft
16 ft × 12 ft = 192 sq ft
-
Rows of boards 26 rows
Each row: 5.5 in board + 0.25 in gap = 5.75 in 144 in of deck width ÷ 5.75 in = 25.04, rounded up to 26
-
Decking needed 416 linear ft
26 rows × 16 ft = 416 ft
-
Boards to buy 29 boards
416 ft × 1.10 (10% waste) = 457.6 ft 457.6 ft ÷ 16 ft per board = 28.6, rounded up to 29
-
Joists 13 joists
192 in of deck length ÷ 16 in spacing = 12 12 + 1 for the far end = 13
-
Deck screws 676 screws
26 rows × 13 joists × 2 screws per crossing = 676
-
Board cost —
Add a price per board to see the cost.
Estimates only. Results come from the formulas listed below and use no outside data. Check local building codes and your supplier before buying.
Your deck
- 26 rows of boards, running along the length
- 13 joists, 16 in apart
How to use the calculator
This deck board calculator works for any rectangular deck with the boards laid straight, in imperial or metric units.
- Measure the deck. Enter the side the boards run along as the length, and the other side as the width.
- Enter the actual width of your deck boards and the gap you will leave between them.
- Pick the board length you will buy and how far apart your joists are, measured center to center.
- Set a waste allowance. The default is 10%.
- Add a price per board if you want a cost estimate.
The results update as you type, and each one shows the sum behind it. Switch to metric at the top of the form if you measure in meters and millimeters. The page address updates too, so you can bookmark or share your numbers.
How the numbers are calculated
- Area is the length times the width.
- Rows of boards: the deck width in inches, divided by one board width plus one gap, rounded up.
- Linear feet of decking: the number of rows times the deck length. It is the total length of board you would have if you laid every row end to end.
- Boards to buy: the linear feet plus the waste allowance, divided by the board length, rounded up.
- Joists: the deck length in inches, divided by the joist spacing, rounded up, plus one for the far end. Each joist is as long as the deck is wide.
- Screws: two screws wherever a row of boards crosses a joist, so rows × joists × 2.
- Cost: the number of boards times the price per board.
Assumptions
- A partial row still needs a whole board, so rows are rounded up: on the 16 × 12 ft example, 144 ÷ 5.75 = 25.04 becomes 26 rows.
- Boards to buy assumes offcuts are reused. The linear feet of every row is pooled before dividing by the board length, so a 12 × 12 ft deck needs 22 boards 16 ft long rather than one board per row (26). For one uncut board per row, pick a board length at least as long as the deck.
- Screws are counted at 2 per board-and-joist crossing, the fastening the American Wood Council's deck guide (DCA 6) gives for wood decking. Hidden fastener clips are counted differently; follow the maker's guide.
- Joists are counted as the deck length divided by the spacing, rounded up, plus one for the far end. Rim joists, doubled joists and blocking are not included.
Rules of thumb
- With 5.5-inch boards and a 0.25-inch gap, a deck needs about 2.09 linear feet of board per square foot, or about 2.3 linear feet with 10% waste.
- Plan on about 3.5 deck screws per square foot with joists at 16 inches.
Worked example
A 16 × 12 ft deck with 5.5-inch boards and a 0.25-inch gap, 16 ft boards, joists at 16 inches and 10% waste:
- Deck area: 192 sq ft 16 ft × 12 ft = 192 sq ft
- Rows of boards: 26 rows Each row: 5.5 in board + 0.25 in gap = 5.75 in 144 in of deck width ÷ 5.75 in = 25.04, rounded up to 26
- Decking needed: 416 linear ft 26 rows × 16 ft = 416 ft
- Boards to buy: 29 boards 416 ft × 1.10 (10% waste) = 457.6 ft 457.6 ft ÷ 16 ft per board = 28.6, rounded up to 29
- Joists: 13 joists 192 in of deck length ÷ 16 in spacing = 12 12 + 1 for the far end = 13
- Deck screws: 676 screws 26 rows × 13 joists × 2 screws per crossing = 676
So you would buy 29 boards, 13 joists and 676 screws.
Boards needed by deck size
With 5.5-inch boards and a 0.25-inch gap, 16 ft boards, joists at 16 inches and 10% waste. Boards run along the first dimension. Enter your own sizes for anything else.
| Deck size | Rows | Linear ft | 16 ft boards | Joists | Screws |
|---|---|---|---|---|---|
| 8 × 8 ft | 17 | 136 | 10 | 7 | 238 |
| 10 × 10 ft | 21 | 210 | 15 | 9 | 378 |
| 12 × 10 ft | 21 | 252 | 18 | 10 | 420 |
| 12 × 12 ft | 26 | 312 | 22 | 10 | 520 |
| 16 × 12 ft | 26 | 416 | 29 | 13 | 676 |
| 16 × 16 ft | 34 | 544 | 38 | 13 | 884 |
| 20 × 16 ft | 34 | 680 | 47 | 16 | 1,088 |
| 20 × 20 ft | 42 | 840 | 58 | 16 | 1,344 |
Common board sizes
Deck boards are sold by a nominal size, but the actual width is smaller. Enter the actual width in the calculator. Wood sizes follow the American Softwood Lumber Standard (PS 20); composite boards vary by maker.
| Nominal size | Actual width | Actual thickness |
|---|---|---|
| 5/4 × 6 (wood decking) | 5.5 in (140 mm) | 1 in |
| 2 × 4 | 3.5 in (89 mm) | 1.5 in |
| 2 × 6 | 5.5 in (140 mm) | 1.5 in |
| 2 × 8 | 7.25 in (184 mm) | 1.5 in |
| 1 × 6 composite (Trex and similar) | 5.5 in (140 mm) | About 1 in; check the maker’s spec |
What this calculator leaves out
- It assumes a rectangular deck.
- Boards are laid straight, not diagonally.
- Joists run across the boards, at right angles to them.
- Rim joists, beams, posts and footings are not included.
- Stairs, railings and hidden fasteners are not included.
- Waste is capped at 25%.
FAQ
How much decking do I need?
A 16 × 12 ft deck with 5.5-inch boards and a 0.25-inch gap needs 29 boards 16 ft long, including 10% waste. To work it out, count the rows of boards across the deck: the deck width in inches divided by one board width plus one gap, rounded up (144 ÷ 5.75 = 25.04, so 26 rows). Multiply the rows by the deck length to get linear feet (26 × 16 = 416), add the waste allowance (416 × 1.1 = 457.6), and divide by the length of board you will buy (457.6 ÷ 16 = 28.6, rounded up to 29). The same deck needs 13 joists at 16 inches and 676 screws. Enter your own sizes in the calculator to get the count for your deck.
How many deck boards per square foot?
With 5.5-inch boards and a 0.25-inch gap, each row covers 5.75 inches, so a deck needs about 2.09 linear feet of board per square foot, or about 2.3 linear feet with 10% waste. The number of boards depends on their length: the 192 sq ft worked example needs 29 boards 16 ft long including 10% waste. Plan on about 3.5 deck screws per square foot with joists at 16 inches.
How many deck boards do I need for a 12×12 deck?
A 12 × 12 ft deck with 5.5-inch boards and a 0.25-inch gap needs 26 rows of boards, or 312 linear feet. With 10% waste that is 29 boards 12 ft long, or 22 boards 16 ft long. With joists at 16 inches it also needs 10 joists and 520 screws.
How far apart should deck joists be?
Closer spacing means more joists: a 16 × 12 ft deck needs 17 joists at 12 inches, 13 at 16 inches and 9 at 24 inches. Joist spacing is measured from the center of one joist to the center of the next, and this calculator lets you choose 12, 16 or 24 inches. The 2021 International Residential Code (Table R507.7) allows 1.25-inch wood decking at 16 inches when the boards run across the joists and rest on three or more of them, and 12 inches when they run diagonally; 2-inch wood decking is allowed at 24 inches. Trex's installation guide gives 16 inches for its 1-inch composite boards on a residential deck, 12 inches at a 45-degree angle, and 12 inches on commercial decks. This calculator does not set a safe spacing: that depends on your decking and local building code, so check the board maker's instructions and your building department before you choose.
How much waste should I allow for decking?
This calculator adds 10% by default and lets you set anything from 0% to 25%. Waste covers offcuts, damaged boards and cutting mistakes. The Decks.com decking calculator adds 10% for boards laid straight across the joists, 15% for boards laid at 45 degrees, and notes that patterns such as herringbone can waste up to 20%. A picture-frame border adds mitred cuts at every corner, so allow the higher figure for it too. On the 16 × 12 ft example, 10% waste raises the order from 26 boards to 29, and 15% raises it to 30.
How many screws do I need for a deck?
A 16 × 12 ft deck needs 676 screws at 2 per board-and-joist crossing: it has 26 rows and 13 joists, and 26 × 13 × 2 = 676, about 3.5 per square foot. To count yours, multiply the rows of boards by the number of joists, then by 2. With joists at 24 inches the same deck has 9 joists and needs 468 screws.
Every answer above uses the formulas in how the numbers are calculated, so you can check it with your own sizes.
Sources
The formulas are arithmetic. The spacings, waste rules and lumber sizes quoted on this page come from these publications; follow them and your local building code over this page where they differ.
- 2021 International Residential Code, Table R507.7 (maximum joist spacing for wood decking), International Code Council. Joist spacing allowed for 1.25-inch and 2-inch wood decking, laid across the joists or diagonally. Local amendments can differ, so check your building department.
- Trex Decking Installation Guide (2022), Trex Company. Joist spacing for composite boards (16 inches residential, 12 inches commercial, 4 inches less at a 45-degree angle) and the minimum 3/16-inch gap between boards.
- DCA 6: Prescriptive Residential Wood Deck Construction Guide (2015), American Wood Council. Two screws or nails where each board crosses a joist, boards gapped about 1/8 inch, and each length of decking resting on at least three joists.
- Deck board and materials calculator, Decks.com. Waste allowances of 10% for boards laid straight, 15% for boards at 45 degrees, and up to 20% for complex patterns.
- American Softwood Lumber Standard, Voluntary Product Standard PS 20, American Lumber Standard Committee. Actual sizes of nominal lumber: a 2 × 6 is 1.5 by 5.5 inches, a 2 × 4 is 1.5 by 3.5 inches, a 2 × 8 is 1.5 by 7.25 inches.
Found a mistake? Send a correction. The About page explains who runs DeckTally and how the calculators are checked.
More deck calculators
Planned next: joist, stair, railing, cost and stain calculators. Suggest one if you need it sooner.
Last reviewed .